1. Field of the Invention
The present invention relates to a clamping device for machine tools which have a movable carriage which is linearly movable on a fixed bed and which needs to be clamped to the fixed bed at a specified position during machining.
2. Discussion of the Related Art
In a lathe, for example, a headstock with a spindle fitted thereto is secured on one side of a fixed bed while a tailstock is provided linearly movable on the other side. A workpiece is retained between the tailstock and a chuck of the headstock to keep the workpiece subjected to machining. In this case, in order to prevent the workpiece from swaying, the tailstock is fixed to the fixed bed with a clamping device.
Japanese Patent Laid-Open Publication No. 2000-263358 discloses a clamping device disposed in a recessed portion of the fixed bed that extends along the direction of motion of the tailstock. A force is applied to the right and left inner walls of the recessed portion by means of a plurality of pistons arranged on the tailstock so that a movable rack fixed to the pistons is engaged with a stationary rack fixed to an inner wall of the recessed portion, thereby firmly positioning the tailstock.
With the adoption of the above-mentioned related art structure, the clamping force is applied to the right and left inner walls of the recessed portion by means of pistons to clamp the tailstock. This structure requires an increased number of pistons to ensure the fixing force, thereby causing an increase in the overall dimension and the number of parts of the clamping device.